Link redundancy

In the latest maintenance release of Netscaler (10.1-120.13), we have added support for the new feature “Link Redundancy”. I will provide an introduction, configuration steps to this feature in this blog.

Link Redundancy (LR) offers the ability of a hot standby link (or channel). During the normal operation, one link/channel will be operational which handles all the traffic. A second link/channel will be designated as the standby. When the primary link/channel goes down or administratively shut down, the standby link/channel will become live and start handling the traffic.

Link redundancy is different from Link aggregation. In link aggregation, all the links which are part of the aggregation group are active simultaneously. Moreover, all the links of the aggregation group are connected to the same peer switch. In case of link redundancy, only primary link is active. Secondary link is in standby mode and becomes active only when primary goes down. Also, primary and standby links/channels are connected to different peer switches in LR.

Link redundancy could be used with one single peer device or with multiple peer devices. As shows in the diagram below, Netscaler is connected to Switches S1 and S2. The link to S1 is primary and the link to S2 is standby. Netscaler will start using S2 link only when S1 link is down. This provides a reliable backup to the Netscaler connectivity.

Link redundancy 1

Link redundancy 2

Link redundancy in HA

As part of the LR feature, we have introduced a parameter called LR Min Threshold. This parameter ensures that when a channel’s available bandwidth drops below the configured minimum threshold limit, the channel is administratively shut down. With LR, the standby channel will take over from the primary channel once min threshold kicks-in. For example, assume that each channel to the remove switch from Netscaler has two 1-gig links. Minimum threshold is configured to be 1.5Gbps. When one link on primary channel goes down, the channel’s available bandwidth is only 1-gig which falls below threshold value. Now, this complete channel is administratively shutdown and the standby channel takes over.

How to configure Link Redundancy on Netscaler?

LR is available by default on the LACP group

To configure minimum threshold on the channel, use the below command

# Set channel <id> -lrMinThroughput <integer>

We can use this feature when there is a requirement for Netscaler to connect to multiple switches for redundancy while avoiding any network loops. Using min threshold parameter, you can switch to alternative channel when the available bandwidth falls below certain level. LR feature offers one more powerful tool on Netscaler to meet the networking requirements.